Communications systems have seen exponential growth in demand for bandwidth by the large and small business communities. Moreover, businesses demand a high level of availability in communications systems. One known measure of availability which communication service providers strive to sustain is “five nines” availability, wherein a communication link may be down for only a few minutes a year.
Free space optics (FSO) and broadband radio are two technologies that have been proposed to meet the demand for bandwidth. FSO, however, while providing “infinite” bandwidth, has some drawbacks. For instance, fog may disperse the light beam, thereby rendering reception impossible for long haul communication. Accordingly, for five nines availability, FSO is primarily used for short links (less than 1.5 km). In Europe, for example, FSO has been deployed for applications such as short hops.
Broadband radio technology, on the other hand, is not hampered by fog as is FSO, and accordingly is more reliable for long haul communication. However, heavy rain tends to degrade radio performance. FSO performance, by contrast, is not as quickly degraded by heavy rain.
FSO with its infinite bandwidth and low availability in fog is gaining some recognition in some short distance applications where the delivery of high bandwidth is required. All the current FSOC systems utilize ON/OFF key modulation scheme. However, higher capacity systems require higher modulation schemes for improved data throughput and better carrier-to-noise ratio (CNR) beyond what the current technology can offer.
In view of the foregoing considerations, a system is called for to address the growing demand for bandwidth, a high level of availability, better throughput, and improvements in CNR.